1. Field of the Invention
The present invention relates to a method for forming a metal interconnection for a semiconductor device, and more particularly, to a method for forming an aluminum layer by an atomic layer deposition method.
2. Description of the Related Art
To complete a highly integrated circuit by integrating a plurality of unit devices, the respective unit devices must be electrically connected. The connection process of the unit devices is referred to as a metal interconnection process. As interconnection materials, aluminum (Al) having low resistivity and good step coverage is most typically used. To form an Al layer, a sputtering method as a physical method and a chemical vapor deposition method as a chemical method have been widely used.
According to the sputtering method, the productivity is high and the Al fabrication process is easy. However, it has a problem of poor step coverage. On the contrary, the chemical vapor deposition method has an advantage in that the step coverage is good. However, according to the chemical vapor deposition method, there is a problem in that the film forming parameters are complex and a coarse Al layer is formed in the case when the Al layer thickness exceeds a predetermined level.
In the sputtering method, the reason for the lowering of step coverage is because of a shadow effect. That is, some stepped parts are can not covered with metal particles, since the metal particles are incident straight forwardly from the upper portion of the step, when the Al layer is formed on an underlying layer having a large step caused by a high aspect ratio contact hole.
The thickness of the metal interconnection film becomes nonhomogeneous locally at the stepped portion due to the shadow effect, which lowers the step coverage. Further, since the aspect ratio increases as the integration level of the device increases, the step coverage further deteriorates.
In the case of forming the Al layer by the chemical vapor deposition method, the nucleation and growth of the Al layer occur irrespective of the step of the substrate surface. Thus, the step coverage is excellent. However, if the thickness of the Al layer exceeds about 1000 A, island-like deposition characteristics are exhibited so that the surface of the Al layer becomes coarse. The coarse Al layer is not suitable for a horizontally long metal interconnection. Also, a contact hole or a via having a large aspect ratio cannot be filled uniformly.
Therefore, to manufacture a metal interconnection for a highly integrated circuit, a new technique which can improve uniformity of an Al layer and has excellent conformality to improve step coverage of the Al layer is required.